What subsurface information is important? :

3 How easy is it to drill to the reservoir?
(Cost of drilling, completing…) What subsurface information is important? What is value of hydrocarbon in place?
(Potential value) How easily can the hydrocarbon flow out the well?
(Cash flow)

Formation evaluation is critical to understanding the reservoir :

4 Formation evaluation is critical to understanding the reservoir How easy is it to drill to the reservoir?
(Cost of drilling, completing…) What is value of hydrocarbon in place?
(Potential value) How easily can the hydrocarbon flow out the well?
(Cash flow)

Slide 5:

5 Introduction
Well logs or wireline logs are continuous recordings of well depth versus different petrophysical characteristics of the rocks through which the well is drilled. There are many types of well logs, depending upon the characteristics of the rock being measured.Logging ObjectivesThe main purpose of well logging is: - to provide data for evaluating petroleum reservoirs. - to aid in testing, completion and repairing of the well.
To calculate the oil reserve in an oil pool we need to know the following.  Thickness of the oil bearing formation.  Porosity of the formation.  Oil saturation.  Lateral extent of the pool.
Logs should always be calibrated with core data to improve interpretations. Wireline Logging

Slide 9:

9 Cased Hole LoggingLogging surveys taken after the casing is lowered are usually categorized as cased hole logs. The surveys included in this group are:  Gamma Ray  Neutron  Temperature  Pulsed Neutron  Cement Bond Log Some of these surveys like the gamma ray, neutron and temperature logs can be run in both open and cased hole wells.

Slide 10:

10 Production LoggingWell logging surveys taken to improve production or repair the well are termed as production logs. Surveys included in this category are:  Flowmeter  Pressure  Temperature  Fluid Density

SOME QUESTIONS ADDRESSED BYLOG INTERPRETATION :

18 SOME QUESTIONS ADDRESSED BYLOG INTERPRETATION Geophysicist / Geologist
Are the tops as predicted?
Are potential zones porous?
Formation intervals?
Lithology?
Hydrocarbons?
What type of hydrocarbons?
Commercial quantities? Reservoir Engineer
How thick is the pay zone?
How homogeneous is the zone?
Porosity?
Permeability?
Production Engineer
Which zone(s) to complete?
What production rates?
Any water production?
Is zone hydraulically isolated?
Will well need stimulation?
What stimulation would be best?

TYPICAL OPEN HOLE WIRELINE COSTS :

LOGGING IS COMPARITIVELY INEXPENSIVE! :

21 LOGGING IS COMPARITIVELY INEXPENSIVE!

Slide 22:

22 Fig. 3.1: A Logging Truck

WIRELINELOGGINGEQUIPMENT :

23 WIRELINELOGGINGEQUIPMENT

Slide 24:

24 Computerized Logging Units (Contd.)Computer-based units offer the following features: All logs are recorded on 4 mm dats. Computer control of the data allows logs to be recorded either logging up or down with all curves on depth. Calibration are performed under programme control and can be performed more quickly, consistently and accurately. Logs can be played back from the data tapes on many different formats. Basic wellsite, processing/analysis of data is available.

CHOOSING A LOGGING TOOL :

33 CHOOSING A LOGGING TOOL It is necessary to choose the right tool to get the desired measurement.
Considerations:
Type of well ( wildcat or development ).
Open hole or cased hole.
Hole conditions ( depth, deviation, hole size, mud type )
Examples:
Oil based mud : Induction tool
Water based salty mud : Laterolog Tool
Formation fluid content (fresh/salt connate water).
Economics (cost of the job, rig time involved).

TYPES OF LOGS TO BE RUN :

34 TYPES OF LOGS TO BE RUN Logging suites generally include one resistivity and one porosity device.
The logging string will also have other tools like the gamma ray, SP and caliper tools.
However, logging suites usually have two porosity devices to give more information about rock type, hydrocarbon type and porosity.
Other considerations – to estimate permeability or to take fluid samples – require other special tools like the formation testers.

Radial Fluid and Resistivity Distribution :

Slide 36:

36 NOMENCLATURE FOR ZONES IN
AND AROUND THE BOREHOLE

TOOL CALIBRATIONS :

37 TOOL CALIBRATIONS A logging tool collects data that are converted to porosity, resistivity, and other values.
Each tool is calibrated to an industry standard.
This ensures that each tool, irrespective of the type of tool or tool history or service company, reads the same value when logging the same formation (normalization may still be required between log).
Check tool calibrations before and after a logging job to ensure good quality log data.

LOG QUALITY CONTROL :

38 LOG QUALITY CONTROL Check all calibrations before and after job.
Record a repeat section of about 200 ft to ensure validity of data and to explain abnormal curve response.
Compare log response with offset well logs.
Keep hole conditions (hole size, mud type, tool centralization) in mind when interpreting log data.
Ensure that logging speeds are as recommended by the service company.